1. Field of the Invention
The present invention relates to a novel process for preparing 2-chloro-5-chloromethylthiazole.
2. Description of the Prior Art
2-chloro-5-chloromethylthiazole is an important compound as an intermediate product in a process for preparing biologically active compounds such as insecticides (see, for example, Japanese Patent Application Laid-Open No. 3-157308 (1991)) It can be prepared by, for example, the following processes.
Japanese Patent Application Laid-Open No.63-83079 (1988) discloses a process for preparing 2-chloro-5-chloromethylthiazole by allowing allyl isothiocyanate to react with chlorinating agent as described in the following scheme (A): 
This process requires a large amount of chlorinating agent and the reaction has to be performed under a high temperature, which produces many by-products. Therefore, it is not so suitable for industrial application.
Alternatively, Japanese Patent Application Laid-Open No. 4-234864 discloses a process for preparing 2-chloro-5-chloromethylthiazole by allowing allyl isothiocyanate derivative to react with chlorinating agent as described in the following scheme (B): 
This process is suitable for industrial application which can be performed using approximately an equal amount of chlorinating agent under moderate condition to give a high yield. However, inert solvent (diluent) such as halocarbon may preferably be used to give a high yield, which requires high production cost.
Japanese Patent Application Laid-Open No. 2000-247963 (2000) discloses a process which involves allowing 2-halogenoallyl isothiocyanate to react with chlorinating agent in a dipolar aprotic solvent such as acetonitrile. This process, however, has a disadvantage that the solvent cannot be reused since it is difficult to separate and collect the solvent such as acetonitrile from water.
Accordingly, a novel process for preparing 2-chloro-5-chloromethylthiazole suitable for industrial application is still needed in which an excess amount of chlorinating agent is not required, moderate conditions can be used to give a high yield, and solvent can be collected easily.
The object of the present invention to provide a novel process for preparing 2-chloro-5-chloromethylthiazole which is suitable for industrial application.
Aromatic hydrocarbons and derivatives thereof (particularly toluene) are reactive with chlorinating agent. The present inventors unexpectedly found, as a result of intense studies, that 2-chloro-5-chloromethylthiazole can be obtained at a high yield by allowing 2-halogeno-allyl isothiocyanate to react with chlorinating agent in the presence of aromatic hydrocarbons which may have one or more substituents, and accomplished the present invention based on the findings.
In other words, the present invention provides:
(1) a process for preparing 2-chloro-5-chloromethylthiazole of the following formula (I): 
xe2x80x83by allowing 2-halogeno-allyl isothiocyanate of the following formula (II): 
xe2x80x83(wherein Hal represents chlorine or bromine) to react with chlorinating agent in the presence of an aromatic hydrocarbons which may have one or more substituents;
(2) the process according to (1) above wherein the aromatic hydrocarbons which may have one or more substituents is toluene, chlorobenzene or dichlorobenzene; and
(3) the process according to (1) above wherein the aromatic hydrocarbons which may have one or more substituents is toluene.
(4) the process according to (1) above wherein Hal in the formula (II) is chlorine.
A 2-halogenoallyl isothiocyanate of the following formula (II): 
(wherein Hal represents chlorine or bromine) is a known compound which can be prepared by any known processes. One unlimiting example of such process involves heating a mixture of 2,3-dihalogeno-1-propene (e.g., 2,3-dichloro-1-propene) with thiocyanate represented by M(SCN)n (wherein M represents metal or ammonium group, and n indicates the valence of M) in the presence of water (see, Japanese Patent Application Laid-Open No. 9-136874 (1997)).
The process according to the present invention may be performed in the presence of an xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d. The aromatic hydrocarbon in the xe2x80x9caromatic hydrocarbon which may have one or more substituentsxe2x80x9d herein may include, for example, benzene, naphthalene and phenanthrene. The xe2x80x9caromatic hydrocarbonxe2x80x9d may be substitutedwith, for example, C1-4 alkyl group (e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl or t-butyl) and/or halogen (e.g., fluorine, chlorine, bromine or iodine) and number of substituents is preferably 1 to 3. Examples of such xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d are toluene, o-, m-, p-xylene and xylene isomeric mixtures, ethylbenzene, cumene, cymene, mesitylene, chlorobenzene, as well as o-, m- or p-dichlorobenzene and isomeric mixtures of dichlorobenzene. Preferable examples of xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d are chlorobenzene, dichlorobenzene (o-, m- or p-dichlorobenzene or mixtures thereof) and toluene, among them toluene is particularly preferable. The xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d may be used alone or in combination of two or more thereof.
Preferably 0.1 to 20 parts and more preferably 0.5 to 5 parts by weight of the xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d may be used relative to 1 part by weight of the above-described 2-halogenoallyl isothiocyanate.
The term xe2x80x9cchlorinating agentxe2x80x9d herein refers to chlorine or a compound which releases chlorine under reaction conditions, such as sulfuryl chloride or phosgene. The chlorinating agent is typically used in an amount of 0.8 to 2 equivalents, preferably 1.0 to 1.5 equivalents, and more preferably 1.05 to 1.30 equivalents relative to the above-described 2-halogenoallyl isothiocyanate.
For example, a reaction process according to the present invention using 2-chloroallyl isothiocyanate as the starting material and sulfuryl chloride as the chlorinating agent can be particularly described with reference to the following scheme. 
The process according to the present invention can be performed, for example, under the following conditions.
The reaction may typically be performed at xe2x88x9260 to 60xc2x0 C., preferably at xe2x88x9210 to 50xc2x0 C. and more preferably at 10 to 40xc2x0 C. though a wide range of temperature may be selected.
The reaction may preferably be performed under atmospheric pressure though reduced, atmospheric or pressurized pressure may be used.
The reaction may typically be performed for from 10 minutes to 50 hours and preferably for 1 to 20 hours.
After reaction completed, 2-chloro-5-chloromethylthiazole can be isolated by any known methods. For example, reaction mixture may be washed with a suitable amount of water, oil layer may be separated and collected, and then the xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d may be removed by, for example, vacuum distillation. The xe2x80x9caromatic hydrocarbons which may have one or more substituentsxe2x80x9d may be collected for recycling.